The invention relates to a method for operating an energy storage device, which is provided with at least a first and at least a second energy storage device element in a motor vehicle, wherein the first and the second energy storage element are connected in series in order to provide nominal voltage.
Batteries are used in motor vehicles to operate a variety of motor vehicle systems. Increasingly, rechargeable energy storage devices are used also to operate the drive systems of motor vehicles, for example in hybrid or pure electric vehicles. In this case, in many of these types of motor vehicles, a battery is charged from the power grid to enable a purely electrical operation of the drives. In order to drive these batteries, direct current chargers are in particular used, which provide direct current to charge the battery with a predetermined voltage. The voltage can be typically be varied within a predetermined range so as to charge the vehicle batteries with different nominal voltages, or the charging voltage can be also varied during the charging operation to enable the fastest possible and/or the most gentle possible battery charging operation.
For vehicles with a high electrical output it may be advantageous to use in the electrical system of the vehicle relatively high voltages, in particular for a traction system of the vehicle, for example voltages of up to 800 Volts to achieve a high efficiency of the drive components, as well as to reduce the line diameter in the electrical system of the vehicle and thus to reduce the weight of the vehicle. At the same time, however, it should be also possible to charge the energy storage device which provides this voltage with direct current charging devices that are commonly used in order to provide for the user many charging options for his motor vehicle. The maximum nominal voltage for an energy storage device of a motor vehicle is thus limited by the usual maximum voltage that is typically provided by charging columns. For example, the maximum charging voltage in the charging columns is limited according to CHAdeMo standard to 500 V. Another standard for charging columns, the CCS standards, permits voltages up to 1,000 V. However, many charging columns according to the CCS standard are also limited to 500 V.
In order to allow charging of energy storage devices of a motor vehicle with as many charging columns as possible, it is therefore necessary to use with the currently available charging infrastructure a nominal voltage of the energy storage device of less than 500 V.
The object of the invention is therefore to specify a method for operating an energy storage device by means of which higher voltages can be provided in an electrical system of a vehicle, wherein at the same time, the charging can be conducted with a plurality of motor vehicle-independent energy sources.